This invention relates to apparatus for processing exposed photographic sheet materials. More particularly, it concerns apparatus for spreading processing fluid uniformly over a photochemical layer or layers on one or more such sheets by progressive pressure applied by rolling surfaces of maximum radii.
Self-developing film units are well known in the instant photography art and most commonly employ an assembly of sheet components sandwiching layered photochemical compositions and various processing adjuncts including a rupturable pod of processing fluid in an amount selected to assure complete coverage of the photochemical layers by the fluid supplied in the pod. The processing fluid pod is traditionally located at the leading end of the film unit in the context of its direction of feed through a processing gap defined by a nip between a pair of processing rollers, for example. Upon entry of the leading edge of the unit into the roller nip, the processing fluid pod is ruptured and the contents thereof spread over the remaining area of the photochemicals carried between the sheets of the film unit.
It has been recognized by those familiar with the instant photography art that a combination of processing fluid rheology and chemical action between the processing fluid and the sheet carried photochemicals results in an optimum photograph where the radius of rolling surface defined by the processing roller pair is enlarged to the maximum extent possible in keeping with the spacial constraints of the apparatus in which the processing apparatus is used. In commercially available, hand-carried, instant cameras designed for self-developing film units, for example, the size of the processing rollers is dictated primarily by the space available in the camera and is limited to a roller diameter requiring several revolutions of the rollers for processing passage of a single film unit through the nip of the rollers. For this reason, it is also very important that the surfaces of the processing rollers be isolated from contact by the processing fluid in order to ensure that the roller surfaces will remain truly cylindrical to be effective in the processing fluid spreading operation. This requirement, in turn, has necessitated preassembly of film units in a manner to assure retention of all processing fluid between the traditional two sheets employed in film units of this type.
In larger industrial and/or institutional types of cameras designed for the use of self-developing film units, the diameter of at least one of the processing rollers has been increased to a point where the length of the film unit is equated to the roller circumference in a manner such that a processing pass of the film unit requires only a single revolution of the large diameter roller. The use of such large diameter processing rollers not only enhances the photographic image obtained as a result of a more uniform spread of the processing fluid, but in addition, allows for a simplified assembly of components in the film unit. In this latter respect, it is to be noted that the quantity of processing fluid supplied in each rupturable pod of each film unit must be more than that needed to cover the image area of the film sheets, thus presenting a problem of how to handle the residual processing fluid. Traditionally, this problem has been approached by providing a processing fluid trap at the trailing end of a preassembled instant film unit, for example. Where single revolution processing rollers have been used, however, the need for the trap has been reduced to a point where residual fluid can be accommodated very simply by a trailing end extension of the film sheets. The danger of the residual processing fluid fouling the roller surfaces is avoided by a pocket in the large diameter roller at the point thereof where the trailing edge of the film unit registers.
While the advantages of large diameter rolling surfaces for processing instant film units have been recognized, there is a need for the attainment of such large diameter surfaces while at the same time reducing the space required for accommodating such surfaces.